THE EFFECTS OF MASHING TEMPERATURE AND MASH THICKNESS ON WORT CARBOHYDRATE

Prévia do material em texto

J. Inst. Brew., March-April, 1991, Vol. 97, pp. 85-92 85
THE EFFECTS OF MASHING TEMPERATURE AND MASH THICKNESS ON WORT CARBOHYDRATE
COMPOSITION
By Robert Muller
(Brewing Research Foundation, Lyttel Hall, Nutfield, Redhill, Surrey, RH1 4HY)
Received 2 My 1990
Temperature and mash thickness are shown to affect both mash performance and enzyme activity. Alpha
amylase was found to be considerably more resistant to heat inactivation than was beta amylase. This
difference was reflected by changes in wort fermentability that were manifest at temperatures below
those which affected levels of extract. Increasing the mashing temperature from 65°C to 80°C had only a
slight effect on extract but reduced wort fermentability from over 70% to less than 30%. At 85°C and over,
when temperature had a significant effect on alpha amylase, as well as on beta-amylase, extract was lost
and starch was present in the wort. Diluting the mash with liquor had a similar effect to that of increasing
temperature on both the amylolytic enzymes and on the mash performance. Thin mashes contained more
starch and fewer fermentable sugars than did thick mashes at the same temperature. These changes can
be related to the stability of the amylolytic enzymes.
Key Words: Alpha amylase, beta amylase. mashing temperature,
mash thickness.
Introduction
In recent years a significant amount of attention has been
directed towards controlling the carbohydrate composition of
wort2-8-16-14. Initially this interest centred on optimising mashing
conditions to ensure complete extraction of the malt with a
maximum conversion to fermentable sugars. The aim was to
produce the greatest quantity of fermentable sugar so that the
final beers would have high alcohol and low carbohydrate
concentrations14'23. This work revealed that it was not possible,
by simply using malt enzymes, to convert all the starch to
fermentable sugars. This could only be achieved by the addition
of enzymes, such as amyloglucosidase, to the brews prior to
fermentation1111918. More recently, the use ofsuperattenuating
yeasts12-"-22 has by-passed the necessity for using exogenous
enzymes. This allowed the appearance ofa new type ofproduct,
the 'lite' or 'diet' beers which contained a much higher
proportion of alcohol compared to carbohydrate than did
normal beers.
The process of mashing relies on the different biochemical
characteristics of the enzymes involved. The enzyme alpha
amylase is largely responsible for the breakdown of starch into
lower molecular weight sugars and dextrins. Some of the
sugars are fermentable but the majority, the dextrins, are
not. The other important enzyme is beta amylase. Although
beta amylase has a limited effect on starch, it can rapidly
break down dextrins to form the fermentable sugar maltose'.
The second important difference between these enzymes is
their thermal stability. Alpha amylase is considerably more
stable than beta amylase at high temperatures. These enzyme
properties could be exploited to control the carbohydrate
composition and fermentability of the final wort. However, the
response of these enzymes to temperature is poorly character
ized. Certainly, in the brewing literature, there is little infor
mation concerning mash performance at temperatures over
75°C. In the past there has been little need to lower the
fermentability ofwort, usually the reverse was desired. There is
now an interest in beers with reduced or low levels of alcohol,
and production of these would benefit from controlled wort
fermentability. Extraction of the malt must not be impaired,
and starch must not appear in the final worts. The present study
establishes mashing regimes that can be used to control wort
fermentability from a maximum down to less than 10%.
Experimental
Small scale mashing was performed using a BRF mashing
bath as described by Buckee et al.6 except that the mash
temperature and thickness were varied. Mashing experiments
using 1.5 kg of malt were performed on the BRF mashing
column described by Bathgate et al3. The measurement of total
carbohydrate levels in wort were performed by the method of
Buckee and Hargitt5, and the levels of fermentable sugars in
wort were determined using HPLC7. For the purposes of these
experiments the levels of starch in worts were defined as carbo
hydrate material that was precipitated from acidified solution
by iodine14.
Estimation of alpha amylase activity was by a modification
of the method of Smith et al2I. Samples were taken from the
B.R.F. mashing column and cooled rapidly on ice; the alpha
amylase was then extracted using the buffers recommended by
Smith etal21. The activity of this extract was determined using
beta-limit dextrin (Rank Hovis) at 35'C. A standard curve of
amylase over a temperature range from 15*C to 40°C was also
prepared and this was used to extrapolate enzyme activity to
65'C. Over the lower temperature range the amylase was
unlikely to suffer from thermal inactivation. Thus the initial
activity at 65*C could be inferred, without encountering
problems caused by heat and damage to the enzyme.
To estimate beta amylase, samples of mash, or ofmalt, were
extracted at an equivalent concentration of 50 g dry matter in
150 ml of mashing liquor. The liquor was adjusted to 30 mM
sodium chloride, 3 mM dithio-threitol, 30 mM ethylenediamine
tetraacetic acid (sodium salt) and 0.06 M acetate at pH 4.8,
(enzyme buffer), by the addition of appropriate volumes of the
concentrated solutions. The mixtures were shaken for one
hour at 2*-4"C and undissolved material was removed by
centrifugation at 2000 x g for 5 minutes. The supernatant
was collected and diluted (with buffer) as required. After
equilibration at 20°C, 1 ml of extract was mixed with 1 ml of
buffer and 1 ml of 2% w/v Lintner starch. After 3 minutes at
20*C, 3 ml of DNS reagent was added. This reagent contained
1% w/v dinitrosalicylic acid (DNS), 1.6% w/v sodium hydrox
ide and 30% w/v potassium sodium tartrate. The mixture was
boiled for 5 minutes and cooled by the addition of 20 ml of
cold water. The absorbance of the mixture was monitored at
540 nm, and the values for unknown samples compared with
the appropriate blanks and standard solutions. Mash liquids
frequently gave very high background values due to the
presence of starch conversion products. These were effectively
removed by dialysis overnight at 4°C, against enzyme buffer.
As with alpha amylase activity, the initial beta amylase
activity at 65°C was inferred from a standard curve. In this case
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86 WORT CARBOHYDRATE COMPOSITION [J. Inst. Brew.
the standards were obtained over the temperature range 10°C
to 30"C.
Laboratory scale fermentations, using one and a half litres of
wort, were performed by the method of Brown and Kirsop4.
Results
The effect of different mashing temperatures on wort
fermentabilily is due to the different properties of the two main
amylolytic enzymes. Figure 1 shows that at 65°C (a typical
mashing temperature) alpha and beta amylases have different
stabilities. In order to achieve a mash stand temperature of
65'C, the liquor temperature was 72"C before striking. The
temperature of the mash was monitored over the sampling
period, the average value being 64.4°C. Samples of the mash
were removed and the enzyme activity determined as described
above. After 60 minutes approximately half of the alpha
amylase activity remained, whilst less than ten per cent of the
original beta amylase activity was present.
The thermal decay of enzymes may be characterized by the
equation A=Aoe~I", where Ao is the initial activity, A is the
activity at time t, and t is the duration of the mash. From the
data shown in Figure 1 the decay constants, k, of malt alpha
and beta amylase activity were calculated. The value for alphaamylase was 0.0163 (r=0.96) and for beta amylase 0.0434
(r=0.98). This demonstrates that alpha amylase is considerably
more stable than beta amylase at 65 C. Although there may be
many potential inaccuracies with these measurements (see
discussion), the equation can be integrated to give an indication
of the total enzymic activity during the mash. The total
potential activity of alpha amylase (adjusted to 65*C) was
87.9 g of starch digested per gram of malt, a level far in excess
of that required to digest the amount of starch actually present.
The total activity of beta amylase was considerably lower at
3.5 g of maltose produced per gram of malt. So not only was
alpha amylase more stable than beta amylase at mashing
temperatures, but loss of some alpha amylase could be
predicted to have less effect on a mash than the loss of beta
amylase.
Figure 2 A-D compares the activity of alpha and beta
amylases in mashes over a range of temperatures from 75°C to
90'C. Again l.S kg of malt were mashed with 3.75 L of water.
The striking temperature of the liquor was adjusted each time
to achieve the desired mash temperature, and was usually 6-TC
higher than the final temperature17.
At 75°C there was significant decay of both enzymes but
considerable amounts of beta amylase were still present at the
end of a 30 minute period. Conversely at 90°C there was
extremely rapid breakdown of both enzymes. Almost all of the
beta amylase was destroyed within 10 minutes but very little
alpha amylase survived after 20 minutes. It remains unlikely
that in such a mash there would be sufficient enzyme activity to
completely digest all of the starch. The greatest difference in
enzyme stability was observed at temperatures between 80 and
85°C. At these temperatures there was essentially complete
inactivation of beta amylase but with sufficient alpha amylase
activity surviving throughout the mash to ensure complete
starch conversion.
The effect on wort properties of a range of mashing tempera
tures is shown in Figure 3 A-C. In view of the dramatic effects
of very high temperatures on enzyme stability (shown in the
previous figure) it was decided to study mashes over the slightly
lower range of 70°C-85°C. In this case laboratory scale mashes
were performed in the BRF mashing bath using SO g of malt
with a range of mash thicknesses from 2:1 to 7:1. All mashes
were cooled and subsequently adjusted to 450 g with water and
filtered. The total carbohydrate, fermentable sugar and starch
Alpha Amylase Activity
1.4r
Beta Amylase Activity
-i80
30 40
Time (mln)
Fig. I. Inactivation of malt amylase mashed at 65*C. Samples of mash were taken from a standard run on the BRF Mashing column using l.S kg
malt mashed with 3.75 litres of water (liquor to grist ratio 2.5:1). Alpha and beta amylases were extracted and their activity determined at a
standard temperature. This activity was corrected to 65°C by extrapolation. Alpha amylase (■ ■) activity is presented as grams of limit
dextrin hydrolysed per minute per gram of malt. Beta amylase (O O) activity is presented as grams of maltose produced per minute per
gram of malt.
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Vol. 97, 1991]
Figure 2A—75°C
120
Activity %
WORT CARBOHYDRATE COMPOSITION
Figure 2B—80°C
87
Time (minutes)
120
Activity %
5 10 16 20 25 30 35 6 10 15 20 25 30 35
Time (minutes)
Figure 2C—85°C
Activity %
120 r
Figure 2D—90'C
Activity %
120
100<>
5 10 16 20 26 30 35
Time (minutes)
5 10 16 20 25 30 36
Time (minutes)
Fig. 2. Enzyme stability in mashes of different temperatures. As for figure I except that the striking temperature of the liquor was adjusted to give
mash stand temperatures of 75'C, 80°C, 85°C and 90'C. In this case the enzyme activities are expressed as a percentage of the original so that
a direct comparison can be made. Alpha amylase (■ ■): beta amylase (O O).
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88 WORT CARBOHYDRATE COMPOSITION [J. Inst. Brew.
Figure 3A [Carbohydrate] %
12r
10
8
6
60 100 160 200 260 300
Water (ml) / Malt (50g)
360 400
Figure 3B Fermentabllity %
80r
60
40
20
60
Figure 3C Starch %
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
100 160 200 260 300
Water (ml) / Malt (50g)
350 400
60 100 160 200 260 300
Water (ml) / Malt (60g)
360 400
Fig. 3. Effect of mashing temperature on the carbohydrate contents of wort. Samples of malt (50 g) were mashed with varying amounts of water
in the BRF mashing bath. After 1 hour at the temperatures shown, the mashes were cooled and adjusted to 450 g with cold water. After
filtration the total carbohydrate levels (3A) were measured by the anthrone reaction. Fermentable sugar levels (3B) were determined by
HPLC and are presented as a percentage of the total carbohydrate level. Wort starch (3C) was measured by iodine precipitation followed by
anthrone reaction. Temperatures: 70°C (■ ■); 75"C (O O); 80°C (A A); 85°C (□ D).
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Vol. 97, 1991] WORT CARBOHYDRATE COMPOSITION 89
levels in the wort were measured using techniques described
above.
The temperature range studied had only a slight effect on the
level of total soluble carbohydrate that could be extracted into
the wort (see Figure 3A). At the lower water to malt ratios
(thicker mashes) there seemed to be more variation with the
lower temperatures yielding carbohydrate levels between 8 and
9 g/100 ml and with the higher temperatures yielding levels
between 9 and 10 g/100 ml. At higher ratios there was less
variation.
The situation was very different where fermentability was
concerned (Figure 3B). At each mash thickness a 5'C increase
in temperature significantly reduced the fermentability of the
final wort. Decreasing the mash thickness also resulted in wort
with lower fermentability. This latter effect was small at 70'C
but a difference of 26% fermentability was obtained at 75'C
between worts from mashes at ratio 2:1 and 7:1. Indeed the
fermentability of wort produced at 75°C and ratio 7:1 (30.3%)
was lower than wort produced at 80°C and a mash thickness of
2:1 (33.8%). A thin mash (7:1) at 85°C yielded wort of only 6%
fermentability, despite of producing good extract levels (Figure
3A). The results for fermentability were mirrored by the wort
starch measurements in thinner mashes where each S'C rise in
temperature increased the levels of wort starch, the difference
between 80° and 85'C being most dramatic (Figure 3C). In
addition at 80' and 85°C there was a significant increase of
starch with decreasing mash thickness, with the effects at 85'C
again being most noticeable. However between mash ratios 2:1
to 3:1 at 70', 75* and 80'C there was very little difference in
wort starch levels.
The effects of mashing temperature on wort sugars were
investigated further using the BRF mashing column. Thus
1.5 kg ofmalt were mashed with 4.5 litres ofwater (ratio 3:1) at
85'C. During the mashing-in process the temperature fell to
80°C, where it was held for 15 minutes. Extending the mashing
time for periods up to 60 minutes did not have any beneficial
effect. Probably by this time most of the starch had already
been digested, and most of the enzymes destroyed.
Figure 4 shows the carbohydrate profiles of worts run from
the BRF mashing column over time. The run off from the
mash was begun after 15 minutes with sparging at the usual
temperature of 72°C. The three parameters shown are total
carbohydrate (as % concentration), wort fermentability (as
fermentable sugars/total carbohydrate * 100%) and the pro
portion of starch (as starch/total carbohydrate x 100%). The
elution profile of total carbohydrate run from themash showed
that the maximum concentration of carbohydrate (21.4 g/
100 ml) was achieved after 40 minutes from the opening of the
taps, and declined thereafter. The fermentability also rose to a
maximum, at 40 minutes, before declining. A second peak
of fermentability occurred at 60 minutes. This second peak
coincided with the passage of the sparge front through the
mash and into the receiving vessel. Wort collected in the first
5 minutes after the taps had been opened contained some
undigested starch. It is likely that this was due to the presence
of starch underneath the false bottom of the mash bed, rather
than the high mashing temperature since cloudy first runnings
were a feature of 65°C mashes also. Undigested starch could be
largely eliminated by recycling the first 5% ofwort to the top of
the mash bed, giving the mash sufficient time to form a good
filter bed, and ensuring that all the wort had the opportunity to
pass through this filter.
The carbohydrate composition of the wort could be further
modified by maintaining it between 70° and 80*C before
boiling. Figure 5 shows the destruction of alpha and beta
amylases in thin solution rather than in a thick mash. At 70'C
tCH2O;Fermentabllity %
36
30
26
20
16
10
6
Starch/tCH2O
-10.07
0.06
0.06
0.04
0.03
0.02
0.01
0 t 20
Taps open
40 60
Time (mln)
80 100
Fig. 4. Analysis of wort run-on*. The BRF mashing column was used to mash 1.5 kg of malt at 80'C. After IS minutes the taps were opened and
Tractions of wort were collected over a period of 80 minutes. From these fractions the total carbohydrate (by anthrone reaction), fermentable
sugars (by HPLC) and starch (by Iodine precipitation) were determined. The fermentable sugars contents are presented here as fermeniability
(fermentable sugars/total carbohydrate) and the starch content as a starch Traction (starch content/total carbohydrate). Total carbohydrate
% (■ ■): Termentability % (D □); starch/total carbohydrate % ((A A).
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90 WORT CARBOHYDRATE COMPOSITION [J. Inst. Brew.
100
Activity %
0 5 10 16 20 26 30 36
Time (minutes)
Fig. 5. Stability of malt amylases in solution. Alpha and beta amylases
were extracted from malt using cold buffers. One hundred milli-
litre volumes were maintained at the appropriate temperature and
sampled for enzyme analysis at various times. Alpha amylase
70*C (■ ■): beta amylase 70°C (O O); alpha amylase
80°C (A A); beta amylase 80*C (D D).
beta amylase was rapidly inactivated but more than 80%
of alpha amylase activity remained after 30 minutes at this
temperature. At 80°C however the breakdown ofalpha amylase
was much more rapid. The results shown in Figure 3B and 3C
have already indicated that the amylase enzymes are less stable
in thinner mashes resulting in lower fermentabilities and higher
levels of starch. A comparison of Figures 2 and 5 shows that
amylases are stabilized by the thicker mash and are very
unstable in a solution such as wort. By maintaining the wort at
a temperature higher than 70°C but lower than 80°C any
remaining beta amylase was rapidly destroyed before it could
produce significant amounts of maltose whilst the alpha
amylase retained sufficient activity to breakdown any remain
ing starch.
Figure 6 shows an HPLC analysis of a wort produced by the
methods described above. Malt (1.5 kg) was mashed with 4.5 L of
water at either 65*C or at 80°C and after a 15 minute mash stand
10 L of wort was collected over a period of 1 hour. Both worts
were boiled for I h. The worts contained the same quantity of
total carbohydrate measured by an anthrone reaction and both
had a specific gravity of 1.040. However, the quantity of ferment
able sugars present in the wort produced at 85°C was consider
ably lower than in the worts produced at 65OC. The total quantity
of glucose in the low fermentability wort was 30% of that in the
normal wort. Similarly the quantity of maltotriose was 23% of
the normal wort. These two sugars give the best indication of the
inactivation of alpha amylase, since they were not products of
beta amylase activity. The low fermentability wort contained
8.6% of the maltose found in the normal wort. Maltose is largely
a product of beta amylase activity which was the main target of
the elevated temperatures. Thus it was the maltose concentration
which was most severely affected. Interestingly the sucrose level
was only reduced to 71.0% since it is largely a product of the
malting process.
The two worts described above were fermented using a
standard BRF ale yeast, NCYC 1681. In addition a quantity of
Quantity
Maltose Concentrations %
Low Fermentablllty
Sucrose
Glucose
Normal
1 Glucose
Sucrose
Maltose
Maltotrlose Maltotriose
Totals
0.17
0.27
0.36
0.14
0.96
0.66
0.38
4.41
0.61
6.96
60 100
Fraction number
160 200
Fig. 6. Wort sugar analysis. Two worts (both 1.040 gravity) were prepared from the BRF mashing column, at 65°C and at 80°C. The individual
fermentable sugars were determined by HPLC in conjunction with standard sugar solutions. Normal wort ( ); wort produced at high
temperature ( ).
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Vol. 97,1991] WORT CARBOHYDRATE COMPOSITION 91
Yeast weight (g)
0.1 r
0.08 -
0.06
0.04 -
0.02 -
20 40
Time (hours)
60
Fig. 7. Yeast growth in low fermentability wort. The two worts from Figure 6 were fermented in 1.5 litre stirred fermenlers using NCYC 1681. In
addition 10 ml of amyloglucosidase (Novo) was added to a third fermenter containing 80°C wort. During the growth period, 10 millilitre
samples were removed, the yeast washed, and the dry weight measured. Normal wort (A A); wort produced at high temperature
(■-—■); wort produced at high temperature and with amyloglucosidase (O O).
amyloglucosidase was added to a third fermentation vessel
containing wort from an 80"C mash. The growth of yeast was
monitored over a period of 72 hours. The fermentation profiles
of the normal wort and wort from an 80°C mash began in a
similar manner (Fig. 7). However, by 24 hours, when the yeast
in the normal wort was growing vigorously, fermentation in the
wort from the 80°C mash was almost complete. The fermen
tation in the normal wort continued for another 24 hours. This
experiment clearly demonstrates that not only does wort from
a high temperature mash appear to be less fermentable from
its chemical analysis but that it indeed supports less yeast
growth. However, when treated with amyloglucosidase, this
wort supported as much, or slightly more, yeast growth as a
normal wort. The action of amyloglucosidase is to generate
fermentable glucose units from the non-fermentable dextrins.
(This can be demonstrated by HPLC analysis but is not
presented here.) This experiment confirms that a large part of
the extract obtained during high temperature mashing was not
fermentable by normal yeast but demonstrates also that some
brewing enzymes, or superattenuating yeast may be able to
utilize the dextrins. The faster rate ofgrowth in the treated wort
was probably due to the greater proportion of glucose formed
by amyloglucosidase activity.
Discussion
Although mashing regimes differ widely between breweries,
in general a brewer does not alter his mashing process on a
routine basis. Certainly a lager malt is mashed differently from
an ale malt, but within these broad groups a brewer will
probably use a standard mashing regime. In fact mashing para
meters can be altered to achieve a desired wort composition.
The two enzymes which are largely responsible for the carbo
hydrate composition ofwort are alpha and beta amylase16. The
sole product of beta amylase activity (in the presence of alpha
amylase) is maltose whilst alpha amylase produces a varietyof
different molecules9. These range from the lower molecular
weight sugars, glucose, maltose and maltotroise, which are
fermentable by most brewing yeasts, to high molecular weight
dextrins which are not. Figure I shows that these two enzymes
have different stabilities at high temperatures. It is important to
realize, in the wider context of mashing, that it is alpha amylase
that is an unusually stable enzyme at high temperatures. The
other enzymes in the mash, including beta amylase, have much
lower thermal stabilities2-23. The data in Figure I can be used to
assess to total enzymic activities available during the mash.
There are a number of potential inaccuracies in such an
exercise; (i) alpha amylase activity was measured at 35°C and
extrapolated to 65°C using a standard curve; (ii) its substrate
was limit dextrin rather than starch; (iii) beta amylase was
measured at 20°C, and also extrapolated to 65°C; (iv) its
substrate in a mash would include dextrins rather than just
starch; (v) both enzymes were measured separately but would
act in concert during mashing and (vi) both were measured in
thin solution rather than a thick mash. Nevertheless these
differences would tend to result in an under estimate, rather
than an over-estimate, of available enzyme activity. The results
shown in Figure 1 suggest that there is considerably more alpha
amylase activity than is needed to completely digest all the
starch in a mash.
The total beta amylase activity would be sufficient for a
normal mash but more susceptible to inactivation by high
temperatures as shown in Figure 2. The difference was most
marked between 80°C and 85°C when beta amylase was rapidly
inactivated but alpha amylase retained considerable activity.
The predicted effect of raising the mashing temperature would
be a shift in wort composition away from the products of beta
amylase (i.e. a mixture of fermentable and non-fermentable
sugars). Figure 3 shows that there was very little difference in
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92 WORT CARBOHYDRATE COMPOSITION [J. Inst. Brew.
the amount ofextract obtained when mashing over the range of
temperatures 70°C to 85°C. The sugar spectrum, however,
changed considerably, giving lower fermentabilities at higher
temperatures. Furthermore, decreasing mash thickness also
reduced the wort fermentability. It is known that dilution of
enzyme systems increases enzyme instability, but, as with
temperature, beta amylase was more susceptible to dilution
than alpha amylase (Figure 3B). This data confirms and
considerably extends the work of MacWilliam el a/.13-14, and of
Young and Briggs23.
The activity of mash enzymes is more susceptible to heat in a
thin solution than in a mash as shown in Figure 5. Even at 80°C
very little alpha amylase survived beyond 10 minutes (unlike
the mash). Nevertheless, this would be sufficient time for the
enzyme to remove any remaining starch. The beta amylase
would be so rapidly inactivated that it would have no effect on
fermentability. As may be expected from the fermentability
data, the wort starch content increases with inactivation of the
enzymes. The biggest changes were seen at 85°C perhaps
because at other temperatures alpha amylase activity compen
sated for loss of beta amylase. This would also explain why
the increase in wort starch was considerably less than the
decrease in wort fermentability for the same temperature
change. Between 65°C and 80°C any loss of beta amylase would
be compensated for by alpha amylase attack on the remaining
starch. However, at 85°C the alpha amylase is also unstable
(Fig. 2) so that changes in mash thickness have a greater effect
on wort starch (Fig. 3C).
MacWilliam el a/.13-14 found similar results working at
temperatures up to 75°C. They found that wort fermentability
fell at temperatures over 63°C, to about 30% at 75°C, and being
90% of the maximum at 67°C. However, these workers used
different malts (rather than a single one) and did not specify
mash thickness, nor did they extend their work beyond 75°C.
Most of the other work on high temperature mashing has
been performed using temperature programmed mashing
systems10-1'■20, in which high temperatures were arrived at
slowly. The process ofstarch conversion can be extremely rapid
and if temperatures are raised slowly then beta amylase would
have sufficient time to convert dextrins to fermentable sugars.
The work described above does not apply to temperature
programmed mashing systems.
Figures 6 and 7 showed typical analytical and process
data for worts obtained by high temperature mashing. All
worts used in these two experiments were of the same gravity
although the wort produced at 80°C contained considerably less
fermentable sugar, and was unable to support full yeast growth.
Such a wort could be converted to a more normal type by the
addition of amyloglucosidase. Superattenuating yeast would
also be able to utilize this wort fully.
Conclusions
The experiments described illustrate how readily wort
parameters, such as total carbohydrate, fermentability and
undigested starch, can be influenced by changes in mashing
temperature and mash thickness. The appearance of starch in
the wort and the loss of extract would be readily noted by
brewers and yet these are not the most easily influenced
parameters. Wort fermentability however is readily altered by
mashing temperature or thickness because of the lability of beta
amylase. Such changes would not be apparent until the end of
fermentation. The relationship between malt enzymes, malt
starch and the final wort composition is complex and affected
by parameters other than mash temperature and mash thick
ness. Further work is required to elucidate such interactions
and to establish the importance of starch availability, gelatiniz-
ation characteristics and the role of starch associated proteins.
Acknowledgements The author would like to thank Mrs D.
Cairncross for excellent technical assistance, Drs E. D. Baxter
and D. R. J. Laws for advice and discussion, and the Director
of the Brewing Research Foundation for permission to publish
this work.
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4. Brown, B. H. & Kirsop, M. L. Journal of the Institute of Brewing,
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